The invention concerns transceivers for wireless optical communication.
Transceivers of this type consist of an optical transmitter and receiver unit. The intensity of the signal from the transmitting unit and the sensitivity of the receiving unit depend on the angular direction and can be described by means of an emission characteristic an optical reception respectively. However, these respective characteristics of current optical emitter and optical receiver elements exhibit fundamental differences.
Transceivers of this kind are being used in IrDA (Infrared Data Association) applications, for example. The IrDA standard has been defined for data transmission via an optical point to point transmission path. Transceivers usually consist of an infrared transmitter, an infrared receiver and an integrated circuit for signal processing.
A transceiver of the described kind normally has defined ports for signal emission and signal detection. These ports are necessary in order to achieve a particular emission characteristic of the transmitting unit and a particular optical reception characteristic of the receiving unit defined in the IrDA standard. The current IrDA standard defines that the emission angle "psgr"S of the emitted signal must have a value of xc2x115 degrees (half power angle), ensuring that in conjunction with the sensitivity of the receiver the range of transmission is at least 1 m. An additional requirement is that the optical reception characteristic (reception angle "psgr"E) of the detector, that is the angle for which an illuminated receiver can be rotated with respect to its optical axis until the detected signal has dropped to half the maximum value (half power), must be xc2x115 degrees. This value also ensures a range of transmission of up to 1 m. However, infrared emitters (e.g., light emitting diode, LED) and infrared receivers (e.g., photodiode, PD) are physically different elements with fundamentally different properties. Furthermore, the emission characteristic (emission angle "psgr"S) and the optical reception characteristic (reception angle "psgr"E), respectively the size of the reception angle and the emission angle are largely dependent on the shape of the housing, the number and arrangement of the transmitting and receiving elements, and above all on the shape and the dimensions of lenses or other optical devices in the signal path. In current transceivers a typical emission angle "psgr"S might be about xc2x125 degrees and the angle of reception "psgr"E might be about xc2x160 degrees.
A disadvantage of current transceivers is the fact that the guaranteed range of transmission is limited to only 1 m. Moreover, both communicating devices must be aligned with each other forming an angle of nominally no more than 15 degrees between their optical axes, also referred to as direct-line-of sight arrangement. This arrangement is sufficient for applications relying only on short-range point-to-point links. However, it is not a solution for multi-user networking applications, for example, in office or classroom environments. Multi-user networking requires a reliable collision avoidance scheme. A primary condition that must be satisfied to achieve this objective is the existence of channel reciprocity, meaning, that each participating station must be able to transmit its signals over the same area over which it is able to receive other stations. This condition requires equal shapes of the station""s emission and reception characteristics, however, as already stated above, basic optical emitter and optical receiver elements exhibit fundamentally different characteristics. In addition, multi-user networking applications require both increased link distance and increased angular coverage. The present invention is aimed at providing a solution for the optical requirements in such applications.
The limitation to a range of transmission of only 1 m in a cone of 15 degrees is dropped in an extension of the IrDA standard (Advanced IR=AIR). This extension specifies a so-called optical parity requirement for transmitter and receiver to enable multi-user networking applications that rely on channel reciprocity conditions to achieve reliable collision avoidance. Optical parity is given when the ratio of the transmitter""s radiant intensity I [mW/sr] and the receiver""s sensitivity S [xcexcA/mW/cm2] is constant and remains constant under all operating conditions, specified for example by temperature, data transmission rates, directions, etc. Prior art and current state-of-the-art infrared transceivers violate the optical parity requirement. With the extended standard it is no longer necessary that the cross-section of the cone be circular. An elliptic cross-section of the cone of the emission characteristic and the optical reception characteristic is sufficient.
It is an object of the present invention to provide optoelectronic transmitters and receivers that allow to extend data transmission to longer distances (xcx9c10 m) and wider angles (up to xc2x1180 degrees).
It is an object of the present invention to provide optoelectronic transmitters and receivers that meet the optical parity requirement in accordance with the collision avoidance mechanism of an RTS/CTS (Request To Send/Clear To Send) media access protocol.
A transmitter according to the present invention has an optical emission characteristic described by an emission angle "psgr"S (herein referred to as transmitter""s half-angle "psgr"S). "psgr"S is the planar angle that defines where the transmitted power is half the power of the power on the transmitter""s optical axis. A receiver according to the present invention has an optical reception characteristic described by a reception angle "psgr"E (herein referred to as receiver""s half-angle "psgr"E), wherein "psgr"E is the planar angle that defines where the sensitivity is half the sensitivity of the receiver""s sensitivity on the optical axis. An inventive transceiver is characterized in that it comprises a transmitter and a receiver, wherein the transmitter""s half-angle "psgr"S is equal or approximately equal to the receiver""s half-angle "psgr"E within the same plane.
One possible implementation is further characterized in that it provides an angular match of the optical emission and reception characteristics over all emission/reception angles in the horizontal plane.
According to another possible implementation, the transmitter and the receiver are constructed in a way that the three-dimensional optical emission characteristic of the transmitter and the three-dimensional optical reception characteristic of the receiver are identical or at least similar.
According to another implementation, the two-dimensional projection of the optical emission characteristic and optical reception characteristic are identical or at least similar.
The advantages offered by this invention consist in the facts that new transceivers and/or communication systems built according to the present invention comply with the optical parity concept promulgated by the new AIR standard. Furthermore, the transceivers and/or communication systems provide for an increased transmission range and angle. It is another advantage that communicating devices equipped with transmitters/receivers of this kind will not need an alignment as accurate as before. Further advantages are addressed in connection with the detailed description.